The present invention relates to the field of tensioning devices for traction drive elements, such as chains or belts, and in particular is directed to tensioning devices used in connection with tensioning the timing chain or belt for an internal combustion engine.
Chain tensioners for traction drive elements for a timing chain or timing belt drive are known and are also used in connection with traction drive elements for various auxiliary units, such as the generator, power steering pump, air conditioning pump as well as other auxiliary units commonly used on internal combustion engines. The know devices, for example such as shown in U.S. Pat. No. 5,720,683 or U.S. Pat. No. 6,406,391 utilize a plunger located within the bore of a fixed housing which acts on a tensioning shoe to press against the inner or outer run of a traction drive element in order to reduce slack and/or skipping of the traction element on a sprocket or toothed pulley. These known devices utilize a spring in order to press the plunger and associated tensioning shoe toward the tension element. However, they generally lack damping features in order to more effectively attenuate vibrations.
Other known tensioners utilize a ratcheting device in connection with the plunger in order to prevent return motion of the plunger once it has extended past an additional detent or notch on the ratchet. Prior art examples include U.S. Pat. No. 7,513,843 and U.S. Pat. No. 7,455,606.
Additionally, other tensioning devices utilize a blade or leaf spring in connection with the tensioning shoe in order to provide the tensioning function, for example as shown in U.S. Pat. No. 6,609,986 and U.S. Pat. No. 5,797,818.
None of these devices provide a controlled damping feature that allows for improved functioning of the tensioning device so that it not only reduces slack in the traction element, but further dampens vibrations.